A cementing bushing, sometimes referred to as a packoff bushing, is used in a liner hanger assembly to seal between the liner and the running tool, which is lowered into the well on a running string. Once properly lowered, cement is discharged through the running string and around the liner in the well bore. The cementing bushing thus provides for the required increase in fluid pressure to pump cement in the well, and subsequently to selectively break the seal between the liner and the running tool.
Prior art cementing bushings use multiple lugs protruding out from the seal body to lock the bushing into the liner. These lugs may be small and limit the cementing pressure capability of the packoff bushing. An operator typically wishes to pick up the running tool after release from the liner hanger, and the running tool slick joint determines the length the running tool can be picked up before the cementing bushing comes out of the liner. If the operator picks up the running tool above a length of the slick joint, the packoff bushing may disengage from the liner hanger and cause a cementing failure. The entire assembly may then have to be retrieved, since it is not possible to regain pressure integrity.
U.S. Pat. Nos. 3,920,057 and 4,281,711 disclose a liner hanger assembly for hanging a liner in a well, with the assembly including a retrievable packoff bushing. A retrievable and re-stabbable cementing bushing is disclosed in U.S. Pat. No. 6,739,398. More particularly, the cementing bushing disclosed in the '398 patent may be pulled out of the liner and re-stabbed into the liner, although the possibility of pressure trapped below the cementing bushing detracts from the reliability of the system. TIW markets liner equipment with a retrievable packoff bushing and Smith International markets a retrievable cementing bushing with locking lugs. Weatherford markets a Nodeco RSM retrievable seal mandrel.
The disadvantages of the prior art are overcome by the present invention, and an improved liner hanger with a lockable and re-latchable cementing bushing is hereinafter disclosed.